The present invention relates to inertia-operated devices for limiting braking pressure in automobiles, intended particularly for braking systems which have separate supply circuits for the front-wheel brakes and the rear-wheel brakes of the vehicle.
The invention relates more particularly to such a limiting device which operates to prevent the rear wheels of the vehicle from locking before the front ones but which also allows the braking pressure in the supply circuit to the rear brakes to be increased when the supply circuit to the front brakes is out of action irrespective the load on the vehicle thus ensuring adequate deceleration.
Inertia-operated braking pressure limiters are known in which a ball-bearing forming a valve moves along a ramp and cuts off the supply to the rear brakes. Devices in which the interruption in the supply depends both on the load carried by the vehicle and on deceleration are generally mounted so as to be capable of angular movement about a transverse axis and the angular position of the device varies in response to means which are sensitive to the load on the axle carrying the braked wheels.
However, such a device calls for pressurised flexible pipes and connectors to be used and there is a danger of these being damaged by repeated bending strains. For this reason it is essential to use a fixed limiter device.
Such a device has already been proposed in which the support which carries the inertia mass is not directly subject to variations in load. To this end, the mass is mounted on an elastically deformable support which co-operates with a regulating member on which the brake-operating pressure acts.
Although the control pressure for the limiter is higher the more the vehicle is loaded, specific levels of both hydraulic pressure and vehicle deceleration are required for the supply to the rear brakes to be cut off. If the vehicle slows down only well after the hydraulic pressure has been applied (braking on wet or icy surfaces), it is possible that the hydraulic pressure level at which the support circuit to the rear brakes is cut off may be too high. This method of operation is liable to prevent the vehicle from being held to a straight path of travel.